Don't.
SQL has string handling which is - at best - poor.
Do that in your presentation language, where it's trivial. Leave SQL to do what it's best at - storing and retrieving data- and do string manipulation in languages which are designed for it!
For example, in C#, it's three lines of code!
string[] words = lineOfText.Split(' ');
Array.Reverse(words);
string reversed = string.Join(" ", words);